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CONTEXT: Although thyroid hormone replacement may improve outcomes in pregnant women with subclinical hypothyroidism (SCH), the extent to which they receive treatment is unknown. OBJECTIVE: To describe levothyroxine (LT4) treatment practices for pregnant women with SCH. DESIGN: Retrospective cohort study. SETTING: Large US administrative claims database. PARTICIPANTS: Pregnant women with SCH defined by untreated TSH 2.5 to 10 mIU/L. MAIN OUTCOME MEASURE: Initiation of LT4 as a function of treating clinician specialty (endocrinology, obstetrics/gynecology, primary care, or other), baseline TSH, patient clinical and demographic factors, and US region. RESULTS: We identified 7990 pregnant women with SCH; only 1214 (15.2%) received LT4. Treatment was more likely in patients with higher TSH, obesity, recurrent pregnancy loss, thyroid disease, and cared for by endocrinologists. Proportion of treated women increased over time; LT4 treatment was twice as likely in 2014 as in 2010. Women in Northeast and West US were more likely to receive LT4 compared with other regions. Asian women were more likely, whereas Hispanic women were less likely, to receive LT4 compared with white women. Endocrinologists started LT4 at lower TSH thresholds than other specialties, and treated women who were more likely to have had recurrent pregnancy loss and thyroid disease than women treated by other clinicians. CONCLUSIONS: We found large variation in the prescription of LT4 to pregnant women with SCH, although most treatment-eligible women remained untreated. Therapy initiation is associated with geographic, clinician, and patient characteristics. This evidence can inform quality improvement efforts to optimize care for pregnant women with SCH.
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OBJECTIVE: To estimate the effectiveness and safety of thyroid hormone treatment among pregnant women with subclinical hypothyroidism. DESIGN: Retrospective cohort study. SETTING: Large US administrative database between 1 January 2010 and 31 December 2014. PARTICIPANTS: 5405 pregnant women with subclinical hypothyroidism, defined as untreated thyroid stimulating hormone (TSH) concentration 2.5-10 mIU/L. EXPOSURE: Thyroid hormone therapy. MAIN OUTCOME MEASURE: Pregnancy loss and other pre-specified maternal and fetal pregnancy related adverse outcomes. RESULTS: Among 5405 pregnant women with subclinical hypothyroidism, 843 with a mean pre-treatment TSH concentration of 4.8 (SD 1.7) mIU/L were treated with thyroid hormone and 4562 with a mean baseline TSH concentration of 3.3 (SD 0.9) mIU/L were not treated (P<0.01). Pregnancy loss was significantly less common among treated women (n=89; 10.6%) than among untreated women (n=614; 13.5%) (P<0.01). Compared with the untreated group, treated women had lower adjusted odds of pregnancy loss (odds ratio 0.62, 95% confidence interval 0.48 to 0.82) but higher odds of preterm delivery (1.60, 1.14 to 2.24), gestational diabetes (1.37, 1.05 to 1.79), and pre-eclampsia (1.61, 1.10 to 2.37); other pregnancy related adverse outcomes were similar between the two groups. The adjusted odds of pregnancy loss were lower in treated women than in untreated women if their pre-treatment TSH concentration was 4.1-10 mIU/L (odds ratio 0.45, 0.30 to 0.65) but not if it was 2.5-4.0 mIU/L (0.91, 0.65 to 1.23) (P<0.01). CONCLUSION: Thyroid hormone treatment was associated with decreased risk of pregnancy loss among women with subclinical hypothyroidism, especially those with pre-treatment TSH concentrations of 4.1-10 mIU/L. However, the increased risk of other pregnancy related adverse outcomes calls for additional studies evaluating the safety of thyroid hormone treatment in this patient population.